Sunday, December 20, 2015

Peach Bark Damage

Weather: Afternoon temperatures didn’t reach 50, so last Sunday’s snow that lay in shadows didn’t melt until yesterday; then it only disappeared from plants, but not from gravel or bricks; last snow 12/13.

What’s still green: Juniper, arborvitae, other evergreens; leaves on yuccas, grape hyacinth, columbine, vinca, hollyhock, winecup mallow, pink evening primrose, Saint John’s wort, snapdragon, coral beardtongue, tansy, anthemis, coreopsis, purple and golden hairy asters; rose stems, June, pampas, and cheat grasses; young seedlings buried under leaves.

What’s blue-green or gray: Leaves on Apache plume, four-winged saltbush, snow-in-summer, flax, pinks.

What’s red or purple: Stems on young peaches, sandbar willow.

What’s blooming inside: Zonal geraniums.

Animal sightings: Rabbits, chickadees.

Weekly update: Everything you read about fruit trees tells you to keep them pruned. I’m not sure if it’s really necessary, if you’re not a commercial grower. It really may be a type of sympathetic magic that follows the form, if I do something, then nature will reciprocate.

My own experience has been, whenever I have branches cut from trees, insects problems follow. The year after I cut branches off the black locusts, trunks started falling from locust borers. Two years ago I had a branch cut from the peach that was blocking the path, and, in 2014, I dealt with bleeding wounds and aphids. A few weeks ago, I saw similar cracks with globs of reddish amber at the edges.

A tree, as mentioned in the post for 19 October 2014, has a very thin layer of living tissue on the perimeter of its wood. Beyond the current year’s active growth lies another layer of dead matter, the bark that protects it from the elements. Between the bark and the current ring is an impenetrable, narrow barrier that stops water, insects and pathogens from getting inside. It contains suberin.

Like the current ring, it is replaced each year and becomes part of the outer bark. As the tree expands in spring, it may split the bark to make room. Pieces may fall away, or fissures may appear, but the suberin layer remains in tact.

When the water barrier is broken, perhaps by an axe, the tree responds by rebuilding it. This rejuvenation is more complete when temperatures are warm. In winter, rapid changes in temperature can also damage the waxy layer. Because it’s cold, the repairs are slower and sometimes patchy with unprotected sections that stay open to attack.

These earlier cracks and wounds, while they scale over, remain weaker surfaces which can be rebroken.

Alan Biggs has determined, in ideal conditions, repairs begin immediately in the area directly under the breach. After 8 days, the boundary cells are lined with suberin. Then, within the next four days, the cells become denser with starch deposits that look like gum, and may appear red when stained.

The day I saw the resinous-looking globules was Friday, December 11 around 4:45 pm. The previous ten days had seen many morning temperatures around 15 degrees F, with afternoons rising to the mid-40s in the shade. Not the sort of days to promote cell division and defense deployment.

However, that particular day was one when a storm was coming our way. Clouds kept temperatures high - they didn’t fall below 42 in the night, rose to about 54, began falling at noon, but didn’t go below 46 that night. I suspect the unusually long number of hours of relative warmth allowed the tree to do emergency repairs.

Now, like a woman who just discovered she’s pregnant and tries to determine when from the current status of the fetus, I counted back 12 days to see if there were any weather conditions which would have injured the tree.

That took me back to the cold front with the rumbling thunder I described in the post two weeks ago. On Sunday, November 29, temperatures again warmed in the night as clouds preceded the cold air mass. Next came rain, and then, in the dark, the front. The next day’s morning temperature as in the mid-20s, but on December 1 it fell to 13.8 on my porch, the coldest yet this season. I suspect that’s when the damage occurred.

Biggs found the healing process is disrupted if the wounds are washed within 72 hours. The water removes the abscisic acid that is the hormone that plants create, in other situations, to seal the junctions between leaves and branches before the leaves fall.

It rained before the wound formed, then rain fell the day after I saw the red globs. The next day, snow filled all the crevices on the branch. When I looked this week, I saw no signs of the globules. I won’t know until spring if the damage was repaired, or if there are fine cracks in the suberin layer.

Arborists give many explanations for why sun scald and cold damage peach bark. They usually point to the fact it often appears on the southwest sides of trees to suggest the alternating temperatures that stimulate sap to flow, then freeze it in place.

Other events they mention are fertilizing or watering late in the season, which stimulates new growth that doesn’t harden off. They also mention over pruning that removes some of the canopy that protects the undergirding branches.

I suspect canopy loss was what hurt my tree. The branch that was cut in 2013 was high and on the east side of the tree. When it was gone, more light bounced off the white stucco wall and may have weakened the bark along the top of the horizontal branches below where the ladybugs appeared in 2014.

At that time, I kept washing the tree, sometimes spraying it with one of the organic soap compounds, trying to kill the invisible aphids. I also treated it with a fungicide. But that was in the spring.

Now, I can’t do anything but wait, and not let them cut any more branches than necessary. Another low growing one has become a serious barrier on the path when it’s raining. But, when the man suggested cutting other branches, I said no.

The tree was planted in 1997. Peaches rarely live more than twenty years. It may collapse anytime. I don’t expect fruit again. The last time it produced hornets flocked to the area and I had to remove everything before it ripened. The tree now lives for aesthetic reasons alone.

Biggs, A. R. "Anatomical and Physiological Responses of Bark Tissues to Mechanical Injury," in R. A. Blanchette and A. R. Biggs, Defense Mechanisms of Woody Plants Against Fungi, 1992.

Wright, R. C., W. M. Peacock, and T. M. Whiteman. Effect on Subsequent Yields of Storing Cut Seed Potatoes at Different Temperatures and Humidities, 1934.

1. Peach in snow earlier this year, 22 January 2015; chickadee at top.

2. Branches in most recent snow, 15 December 2015. You can see that all the branches are seamed from bark expansion.

3. Pealing bark, 20 December 2015. The under layer is brown and dead.

4. Globules from injuries last year, 12 May 2014.

5. Globular remains after last Sunday’s snow on open wound, 20 December 2015.

6. Ladybugs signally aphids were attacking last year, 29 May 2014.

7. Eighteen-year-old tree in full leaf, 19 September 2015. The damaged area is toward the back and near the house.

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